To study the efficacy of thallium-201 as tumor seeking agent and to study its role in therapeutic response

Abstract

Background: Tumour seeking characteristics of TL-201 have been underutilized. The study was undertaken to evaluate the role of TL-201 scintigraphy in tumour imaging.

Methods: A total of 50 cases were studied over a period of 18 months (13 lymphomas, 11 breast carcinoma, 10 lung cancer, 6 of soft tissue sarcoma, 2 bone tumours and 4 cases each of thyroid and brain tumours). Thallium-201 chloride was injected IV in the dose range of 3-5 mCi. Imaging was done using Siemen's ECAM dual headed gamma camera. Mean tumour to background ratio (T/B ratio) was calculated for all the positive cases. Descriptive statistical analysis was carried out.

Results: Findings revealed a sensitivity of 94.12%, specificity 87.5%, PPV 94.12%, NPV 87.50% and accuracy of 92% for TL-201 tumour imaging. The mean T/B ratio for the true positive cases at 10 min and at 3 h was 1.81 and 1.99 respectively, the difference being 0.18 (P value <0.001). Amongst them, the mean T/B ratios for low-grade tumours were 1.45 ± 0.32 at 10 min and 1.63 ± 0.38 after 3 h with difference of 0.176 (P < 0.001). For the high-grade tumours the ratios were 2.08 ± 0.35 and 2.26 ± 0.41 respectively with a difference of 0.186 (P < 0.001).

Conclusion: Thallium-201 scintigraphy is a useful tumour imaging modality in cases of thyroid, breast, brain, lung, soft tissue and bone tumours and lymphomas. A T/B ratio of 1.63 ± 0.38 in 3 h-delayed imaging is suggestive of low-grade tumours. For high-grade tumours a ratio of 2.26 ± 0.41 should be considered significant.

Keywords: Scintigraphy; T/B ratio; Thallium.

Fig. 1

Benign breast nodule right where the thallium scan is negative. There is no abnormal uptake seen in the right breast.

Fig. 2

NSCLC right lung – false negative thallium scan. There is no abnormal uptake seen in the right lung.

Fig. 3

Carcinoma right breast (operated). Thallium scan showing uptake in the outer quadrant of right breast with T/B ratio of 2.5. Relapse was confirmed by biopsy.

Fig. 4

Glioblastoma multiforme (operated). Scan shows abnormal uptake in the left parietal region with an early T/B ratio of 1.6 and late ratio of 2.5.

Fig. 5

NSCLC left lung post surgery and post chemotherapy. Thallium scan shows uptake in the left lower lobe with an early T/B ratio of 2.3 and late T/B ratio of 2.5.

Fig. 6

Astrocytoma right frontal region. Scan reveals no abnormal focus of uptake.

Fig. 7

Thallium scan shows hot focus in the amputation stump with a T/B ratio of 1.2. The histopathology revealed only granulation tissue.

Fig. 8

Low-grade carcinoma right breast. Thallium scan showing low uptake.

Fig. 9

High-grade carcinoma right breast. Thallium scan showing high uptake.